Mohamed massege to roman Emperor:
In the name of God, the Gracious One, the Merciful
From Muhammad, servant of God and His apostle to Heraclius, premier of the Romans:
Peace unto whoever follows the guided path!
Thereafter, verily I call you to the call of peace. Establish peace and shall have peace. God shall compensate your reward two-folds. But if you turn away, then upon you will sins of Arians (Christian minority).
Then "O People of the Scripture, come to a term equitable between us and you that we worship none but God and associate with Him nothing, and we take not one another as Lords apart from God. But if they turn away, then say: Bear witness that we peace makers."[Quran 3:64]
Seal: Muhammad, Apostle of God
https://en.wikipedia.org/wiki/Muhammad%27s_letters_to_the_heads_of_statethat why the prophet muhammad mentioned the arian christian in name in his message to heraclius!